上次写了hive metastore的partition的生命周期，但是简略概括了下alter_partition的操作，这里补一下alter_partition,因为随着项目的深入，发现它涉及的地方较多，比如insert into 时如果路径存在情况下会调用alter_partition,调用insert overwrite语句时，也会调用该方法，
入口依旧是Hive.java这个类：
1 public void alterPartition(String dbName, String tblName, Partition newPart)
2 throws InvalidOperationException, HiveException {
3 try {
4 // Remove the DDL time so that it gets refreshed
5 if (newPart.getParameters() != null) {
6 newPart.getParameters().remove(hive_metastoreConstants.DDL_TIME);
7 }
8 newPart.checkValidity();
9 getMSC().alter_partition(dbName, tblName, newPart.getTPartition());
10
11 } catch (MetaException e) {
12 throw new HiveException("Unable to alter partition. " + e.getMessage(), e);
13 } catch (TException e) {
14 throw new HiveException("Unable to alter partition. " + e.getMessage(), e);
15 }
16 }
随后通过HiveMetaStoreClient调用alter_partition请求服务端，传入的参数中包含新的partition，然后服务端调用了rename_partition方法，详细不再说了，上一篇大体的也说明了，这里直接从alterHandler.alterPartition进行partition的更改开始。
1 public Partition alterPartition(final RawStore msdb, Warehouse wh, final String dbname,
2 final String name, final List<String> part_vals, final Partition new_part)
3 throws InvalidOperationException, InvalidObjectException, AlreadyExistsException,
4 MetaException {
5 boolean success = false;
6
7 Path srcPath = null;
8 Path destPath = null;
9 FileSystem srcFs = null;
10 FileSystem destFs = null;
11 Partition oldPart = null;
12 String oldPartLoc = null;
13 String newPartLoc = null;
14
15 // Set DDL time to now if not specified
16 if (new_part.getParameters() == null ||
17 new_part.getParameters().get(hive_metastoreConstants.DDL_TIME) == null ||
18 Integer.parseInt(new_part.getParameters().get(hive_metastoreConstants.DDL_TIME)) == 0) {
19 new_part.putToParameters(hive_metastoreConstants.DDL_TIME, Long.toString(System
20 .currentTimeMillis() / 1000));
21 }
22
23 Table tbl = msdb.getTable(dbname, name);
24 //alter partition
25 if (part_vals == null || part_vals.size() == 0) {
26 try {
27 oldPart = msdb.getPartition(dbname, name, new_part.getValues());
28 if (MetaStoreUtils.requireCalStats(hiveConf, oldPart, new_part, tbl)) {
29 MetaStoreUtils.updatePartitionStatsFast(new_part, wh, false, true);
30 }
31 updatePartColumnStats(msdb, dbname, name, new_part.getValues(), new_part);
32 msdb.alterPartition(dbname, name, new_part.getValues(), new_part);
33 } catch (InvalidObjectException e) {
34 throw new InvalidOperationException("alter is not possible");
35 } catch (NoSuchObjectException e){
36 //old partition does not exist
37 throw new InvalidOperationException("alter is not possible");
38 }
39 return oldPart;
40 }
。。。。。。
从代码中我们可以看到:
1、通过Table tbl = msdb.getTable(dbname, name); get到该表的整个元数据的封装信息。
2、随后oldPart = msdb.getPartition(dbname, name, new_part.getValues());，通过dbName、tableName、Values获取partition的元数据信息，Values便是新的partition分区结构eg:（2017-09-11）,随后调用MetaStoreUtils.requireCalStats(hiveConf, oldPart, new_part, tbl)，进行元数据存在校验，如果不存在，则调用updatePartitionStatsFast进行更新（这里就不再详细说明，因为我不知道里面StatsSetupConst的配置参数是干嘛的哈哈哈哈哈~尴尬~一步步来嘛）
3、随后调用了updatePartColumnStats方法，进行物理partition地址的更新，我们一步一步看，代码如下：
1 private void updatePartColumnStats(RawStore msdb, String dbName, String tableName,
2 List<String> partVals, Partition newPart) throws MetaException, InvalidObjectException {
3 dbName = HiveStringUtils.normalizeIdentifier(dbName);
4 tableName = HiveStringUtils.normalizeIdentifier(tableName);
5 String newDbName = HiveStringUtils.normalizeIdentifier(newPart.getDbName());
6 String newTableName = HiveStringUtils.normalizeIdentifier(newPart.getTableName());
7
8 Table oldTable = msdb.getTable(dbName, tableName);
9 if (oldTable == null) {
10 return;
11 }
12
13 try {
14 String oldPartName = Warehouse.makePartName(oldTable.getPartitionKeys(), partVals);
15 String newPartName = Warehouse.makePartName(oldTable.getPartitionKeys(), newPart.getValues());
16 if (!dbName.equals(newDbName) || !tableName.equals(newTableName)
17 || !oldPartName.equals(newPartName)) {
18 msdb.deletePartitionColumnStatistics(dbName, tableName, oldPartName, partVals, null);
19 } else {
20 Partition oldPartition = msdb.getPartition(dbName, tableName, partVals);
21 if (oldPartition == null) {
22 return;
23 }
24 if (oldPartition.getSd() != null && newPart.getSd() != null) {
25 List<FieldSchema> oldCols = oldPartition.getSd().getCols();
26 if (!MetaStoreUtils.areSameColumns(oldCols, newPart.getSd().getCols())) {
27 updatePartColumnStatsForAlterColumns(msdb, oldPartition, oldPartName, partVals, oldCols, newPart);
28 }
29 }
30 }
31 } catch (NoSuchObjectException nsoe) {
32 LOG.debug("Could not find db entry." + nsoe);
33 //ignore
34 } catch (InvalidInputException iie) {
35 throw new InvalidObjectException("Invalid input to update partition column stats." + iie);
36 }
37 }
5、Table oldTable = msdb.getTable(dbName, tableName);这里获取oldTable的所有元数据信息，随后通过makePartName拼接新老partition的partName(eg:/dt=2017-09-11/hour/1)用于新老partition的hdfs的路径对比，因为alterPartition操作，可能是通过alter table、table rename等操作执行的，所以如果老的dbName、tableName、以及partition Name与新的不同，那么就需要将元数据中类似于meta_partition的数据清空。随后通过客户端重新创建partition。
6、如果是相同的，那么说明修改是partition的列信息，通过MetaStoreUtils.areSameColumns(oldCols, newPart.getSd().getCols())进行校验（内部方法不再把代码贴出来了）
7、调用updatePartColumnStatsForAlterColumns开始进行column的更新，这里面代码还是要贴出来一起玩一下：
private void updatePartColumnStatsForAlterColumns(RawStore msdb, Partition oldPartition,
String oldPartName, List<String> partVals, List<FieldSchema> oldCols, Partition newPart)
throws MetaException, InvalidObjectException {
String dbName = oldPartition.getDbName();
String tableName = oldPartition.getTableName();
try {
List<String> oldPartNames = Lists.newArrayList(oldPartName);
List<String> oldColNames = new ArrayList<String>(oldCols.size());
for (FieldSchema oldCol : oldCols) {
oldColNames.add(oldCol.getName());
}
List<FieldSchema> newCols = newPart.getSd().getCols();
List<ColumnStatistics> partsColStats = msdb.getPartitionColumnStatistics(dbName, tableName,
oldPartNames, oldColNames);
assert (partsColStats.size() <= 1);
for (ColumnStatistics partColStats : partsColStats) { //actually only at most one loop
List<ColumnStatisticsObj> statsObjs = partColStats.getStatsObj();
for (ColumnStatisticsObj statsObj : statsObjs) {
boolean found =false;
for (FieldSchema newCol : newCols) {
if (statsObj.getColName().equals(newCol.getName())
&& statsObj.getColType().equals(newCol.getType())) {
found = true;
break;
}
}
if (!found) {
msdb.deletePartitionColumnStatistics(dbName, tableName, oldPartName, partVals,
statsObj.getColName());
}
}
}
} catch (NoSuchObjectException nsoe) {
LOG.debug("Could not find db entry." + nsoe);
//ignore
} catch (InvalidInputException iie) {
throw new InvalidObjectException
("Invalid input to update partition column stats in alter table change columns" + iie);
}
}
这里可以看到，它查询元数据并封装了一个ColumnStatistics对象，这个对象主要封装了tableName、PartName、colName等信息，随后将其取出来使新老ColName进行对比，注意，这里是对colName以及type进行对比，如果不同，则删除老的colName信息。
好的，现在相当于将所有old的不一致的数据删除，下来我们回到之前的alterPartition中来，随后调用alterPartition(dbname, name, new_part.getValues(), new_part)将新的partition数据注册到元数据中。以上，只是当调用rename_partition时，par_vals为null的情况下，对oldPart所进行的操作，那么不为null时呢？是不是很绝望？我们慢慢折磨哈哈。。。
8、在par_vals不为null的情况下，会通过dbName、tableName、以及part_vals进行oldPart的查找并进行校验。
9、对表的类型进行判断，如果该表为内部表，则将原有的oldPart的table所在storage路径，也就是hdfs路径赋给newPart,这里注意的是不是partition的location路径，是storage的location路径。随之调用deletePartitionColumnStatistics直接删除原有partition meta信息。
10、如果该表为外部表，其实就是进行check,随后删除元数据meta(其实是中间有没懂得地方哈哈哈。。而且太晚了，后续补上....)代码如下：
1 try {
2 destPath = new Path(wh.getTablePath(msdb.getDatabase(dbname), name),
3 Warehouse.makePartName(tbl.getPartitionKeys(), new_part.getValues()));
4 destPath = constructRenamedPath(destPath, new Path(new_part.getSd().getLocation()));
5 } catch (NoSuchObjectException e) {
6 LOG.debug(e);
7 throw new InvalidOperationException(
8 "Unable to change partition or table. Database " + dbname + " does not exist"
9 + " Check metastore logs for detailed stack." + e.getMessage());
10 }
11 if (destPath != null) {
12 newPartLoc = destPath.toString();
13 oldPartLoc = oldPart.getSd().getLocation();
14
15 srcPath = new Path(oldPartLoc);
16
17 LOG.info("srcPath:" + oldPartLoc);
18 LOG.info("descPath:" + newPartLoc);
19 srcFs = wh.getFs(srcPath);
20 destFs = wh.getFs(destPath);
21 // check that src and dest are on the same file system
22 if (!FileUtils.equalsFileSystem(srcFs, destFs)) {
23 throw new InvalidOperationException("table new location " + destPath
24 + " is on a different file system than the old location "
25 + srcPath + ". This operation is not supported");
26 }
27 try {
28 srcFs.exists(srcPath); // check that src exists and also checks
29 if (newPartLoc.compareTo(oldPartLoc) != 0 && destFs.exists(destPath)) {
30 throw new InvalidOperationException("New location for this table "
31 + tbl.getDbName() + "." + tbl.getTableName()
32 + " already exists : " + destPath);
33 }
34 } catch (IOException e) {
35 throw new InvalidOperationException("Unable to access new location "
36 + destPath + " for partition " + tbl.getDbName() + "."
37 + tbl.getTableName() + " " + new_part.getValues());
38 }
39 new_part.getSd().setLocation(newPartLoc);
40 if (MetaStoreUtils.requireCalStats(hiveConf, oldPart, new_part, tbl)) {
41 MetaStoreUtils.updatePartitionStatsFast(new_part, wh, false, true);
42 }
43 String oldPartName = Warehouse.makePartName(tbl.getPartitionKeys(), oldPart.getValues());
44 try {
45 //existing partition column stats is no longer valid, remove
46 msdb.deletePartitionColumnStatistics(dbname, name, oldPartName, oldPart.getValues(), null);
总的来说，会发现调用alterPartition的时候，并没有与物理操作耦合在一起，只是对ColumnStats元数据进行查找更新删除等动作，但是真正在调用alterPartition时，对于元数据本身，其实是更新了该partition的sd信息，以及重要的location.
相关的操作还是蛮多的，这里知识大致的分析了下，边看源码边写， 如有错误之处，还望各位大神之处，谢谢~ 碎觉~~明天去作死的干活咯~
